Numerical simulations towards optimizing the burner design for efficient staged pressurized oxy-coal combustion.

Abstract

Staged pressurized oxy-coal combustion (SPOC) – a technology developed at Washington University at St. Louis (WUSTL) – is nowadays a promising tool for low-cost/emissions, high-efficiency power generation. The present computational simulations, performed at West Virginia University (WVU) by means of the ANSYS Fluent package, compliment the experimental research for better understanding of the impacts of turbulence, fluid flow, flame/particle dynamics, and heat transfer on oxy-coal combustion. Here, CO₂ is injected alongside the coal, for its carriage, while a small amount of CH₄ is also injected alongside the coal to maintain a steady flame. Out of 100 kW in a lab-scale reactor, 10 kW originates from CH₄-air burning and 90 kW comes from coal combustion. Steady and unsteady RANS simulations are performed resulting in an asymmetric flame shape. Three causes of the flame asymmetry are hypothesized: (i) coal injection, (ii) onset of the shear-layer instability due to various stream velocities and densities in a shear layer, where mixing occurs, and (iii) presence of the vortex shedding due to the flow past a bluff body, which is used to stabilize the flame. As a result, an impact of the presence of coal on the flame symmetry is demonstrated, and a benchmark at which further increase of coal would result in flame asymmetry is found. The present simulations also shows occurrence of the vortex shedding when the flow passes over a disk in the reactor used to stabilize the flame, constituting a potential reason for the periodic flame oscillations experienced in the result.

This work is performed in cooperation with the Washington University at St. Louis (WUSTL). It is sponsored by the US Department of Energy (DoE) through the US-China Clean Energy Research Center – Advanced Coal Technology Consortium (CERC-ACTC).